This invention relates to antifouling coatings, and more particularly to a method for inhibiting the fouling of aluminum and aluminum-base alloy structures.
The protection generally used to prevent ship fouling by barnacles and other marine organisms is to cover those portions exposed to attack with paints containing antifouling compounds. Recent developments have shown that fouling is effectively prevented by the use of organometallic compounds containing tin, often incorporated into a paint. While paints are effective they do suffer from several drawbacks. For example, the rate of leaching of the antifouling compounds from the paints increases with the speed of the craft. This is undesirable, because the effective life of the coating is shortened and the coating must be reapplied. Further, since the antifouling compounds are diluted by their mixture with paint, the concentration of the compound per unit of exposed area is decreased, thereby decreasing the effectiveness for a given amount of compound. To be effective, the concentration of the antifouling ingredient in the paint should be greater than about 30% to 40% by weight. This high concentration combined with the high rate of leaching could have a detrimental effect on the environment. In addition, the shear forces generated by a ship moving through water cause peeling of the paints, leaving unprotected areas exposed to fouling.
In buried pipeline applications, prior art practices have included the use of copper-nickel pipes which are inherently antifouling. Aluminum pipes have the advantage of being light-weight, but they are prone to fouling.
Thus, there is a need for an antifouling coating to decrease the drag produced by the attachment of barnacles and other organisms to marine craft, and to prevent the fouling of buried aluminum pipelines, without the disadvantages of dilution, peeling, high rate of leaching, and adverse environmental effects.